Preparation of N-doped Porous Carbon from Porous Organic Framework for Gas Sorption

Abstract

In this report, a series of N-doped porous carbon materials were successfully prepared from nitrogen-containing porous organic framework JUC-Z2. Compared to original JUC-Z2, the carbonized samples show obviously enhanced gas uptake and isosteric heats of adsorption (Q<inf>st</inf> for short). Among the carbonized samples, JUC-Z2-900 shows high CO<inf>2</inf> uptake of 113 cm³·g^-1 at 273 K and 1 bar and H<inf>2</inf> sorption of 246 cm³·g^-1 at 77 K and 1 bar, surpassing most reported porous materials. Especially for CH<inf>4</inf> sorption, a large sorption amount of 60 cm³·g^-1 could be achieved at 273 K and 1 bar. To our best knowledge, this value is comparable to the highest among all the porous materials reported to date. Apart from high gas uptake, the carbon materials also show selective adsorption ability. At 273 K, JUC-Z2-900 shows a high CO<inf>2</inf>/N<inf>2</inf> adsorption selectivity of 10 and CO<inf>2</inf>/H<inf>2</inf> adsorption selectivity of 66. Raman spectra showed two Raman shifts, the G-band at 1590 cm^-1 is associated with the E<inf>2g</inf> mode of graphite, whereas the D-band centered at around 1360 cm^-1 is attributed to the D-band of disordered carbon, corresponding to the defect-induced mode. The intensity of D-band is higher than G-band, indicating a low degree of graphitization. This is also confirmed by powder X-ray diffraction results. X-ray Photoelectron Spectroscopy (XPS) results indicate the nitrogen content is 3.26 wt%, 2.88 wt% and 2.19 wt% for JUC-Z2-700, JUC-Z2-800 and JUC-Z2-900 respectively. Though the nitrogen content decreased after carbonization, the gas sorption increased greatly. This can be attributed to the increased heat of adsorption of the carbonized samples. First, the narrow pore size after carbonization is beneficial for gas storage. Reports indicate that by tuning the pore sizes to around the kinetic diameter of CO<inf>2</inf>, it may be possible to increase the number of double or multiple interactions between the adsorbed CO<inf>2</inf> and the pore walls. Second, the all-carbon-scaffold networks also benefit the gas-adsorbent interaction. Last but not the least, the N-doped framework also devote the high gas uptake. Besides the high gas uptake, the carbon materials exhibit high thermal stabilities and could be stable up to 500℃. Based on the above results, the carbon materials show great potential in the fields of CO<inf>2</inf> capture and clean energy storage.